Term | Definition |
Membrane Proteins | • Allow communication with environment
• ½ mass of plasma membrane
• Most specialized membrane functions
• Some float freely
• Some tethered to intracellular structures
• Two types:
– Integral proteins; peripheral proteins |
Membrane Lipids | • 75% phospholipids (lipid bilayer)
– Phosphate heads: polar and hydrophilic
– Fatty acid tails: nonpolar and hydrophobic
5% glycolipids
• – Lipids with polar sugar groups on outer
membrane surface
• 20% cholesterol
– Increases membrane stability |
Plasma Membrane | • Lipid bilayer and proteins in constantly
changing fluid mosaic
• Plays dynamic role in cellular activity
• Separates intracellular fluid (ICF) from
extracellular fluid (ECF)
– Interstitial fluid (IF) = ECF that surrounds
cells |
Generalized Cell | • All cells have some common structures
and functions
• Human cells have three basic parts:
– Plasma membrane—flexible outer boundary
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– Cytoplasm—intracellular fluid containing
organelles
– Nucleus—control center |
Cell Diversity | • Over 200 different types of human cells
• Types differ in size, shape, subcellular
components, and functions |
Cell Theory | • Organismal functions depend on individual
and collective cell functions
• Biochemical activities of cells dictated by
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their shapes or forms, and specific
subcellular structures
• Continuity of life has cellular basis |
Cell | structural and functional unit of life |
Membrane Proteins | • Integral proteins
– Firmly inserted into membrane (most are
transmembrane)
– Have hydrophobic and hydrophilic regions
• Can interact with lipid tails and water
Membrane Proteins
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– Function as transport proteins (cha |
Membrane Proteins | • Peripheral proteins
– Loosely attached to integral proteins
– Include filaments on intracellular surface for
membrane support
Function as enzymes; motor proteins for
Membrane Proteins
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– shape change during cell divi |
Six Functions of Membrane Proteins | 1. Transport
2. Receptors for signal transduction
3. Attachment to cytoskeleton and
extracellular matrix
4. Enzymatic activity
5. Intercellular joining
6. Cell-cell recognition |
Lipid Rafts | • ~20% of outer membrane surface
• Contain phospholipids, sphingolipids, and
cholesterol
• More stable; less fluid than rest of
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membrane
– May function as stable platforms for cellsignaling
molecules, membrane invagin |
The Glycocalyx | • "Sugar covering" at cell surface
– Lipids and proteins with attached
carbohydrates (sugar groups)
• Every cell type has different pattern of
sugars
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– Specific biological markers for cell to cell
recognition
– Allow |
Cell Junctions | • Some cells "free"
– e.g., blood cells, sperm cells
• Some bound into communities
– Three ways cells are bound:
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• Tight junctions
• Desmosomes
• Gap junctions |
Cell Junctions: Tight Junctions | • Adjacent integral proteins fuse |
Cell Junctions: Desmosomes | • "Rivets" or "spot-welds" that anchor cells
together at plaques (thickenings on
plasma membrane)
– Linker proteins between cells connect plaques
Keratin filaments extend through cytosol to
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– opposite plaque giving sta |
Cell Junctions: Gap Junctions | • Transmembrane proteins form pores
(connexons) that allow small molecules to
pass from cell to cell
– For spread of ions, simple sugars, and other
small molecules between cardiac or smooth
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muscle cells |
Plasma Membrane | • Cells surrounded by interstitial fluid (IF)
– Contains thousands of substances, e.g.,
amino acids, sugars, fatty acids, vitamins,
hormones, salts, waste products
• Plasma membrane allows cell to
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– Obtain from IF exac |
Membrane Transport | • Plasma membranes selectively
permeable
– Some molecules pass through easily; some
do not
• Two ways substances cross membrane
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– Passive processes
– Active processes |
Types of Membrane Transport | • Passive processes
– No cellular energy (ATP) required
– Substance moves down its concentration
gradient
Active processes
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• – Energy (ATP) required
– Occurs only in living cell membranes |
Passive Processes | • Two types of passive transport
– Diffusion
• Simple diffusion
• Carrier- and channel-mediated facilitated diffusion
• Osmosis
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– Filtration
• Usually across capillary walls |
Passive Processes: Diffusion | • Collisions cause molecules to move down
or with their concentration gradient
– Difference in concentration between two
areas
• Speed influenced by molecule size and
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temperature |
Passive Processes | • Molecule will passively diffuse through
membrane if
– It is lipid soluble, or
– Small enough to pass through membrane
channels or
Passive Processes
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channels, – Assisted by carrier molecule |
Passive Processes: Simple Diffusion | • Nonpolar lipid-soluble (hydrophobic)
substances diffuse directly through
phospholipid bilayer
– E.g., oxygen, carbon dioxide, fat-soluble
vitamins |
Passive Processes: Facilitated Diffusion | • Certain lipophobic molecules (e.g.,
glucose, amino acids, and ions)
transported passively by
– Binding to protein carriers
Moving through water filled channels |
Carrier-Mediated Facilitated Diffusion | • Transmembrane integral proteins are
carriers
• Transport specific polar molecules (e.g.,
sugars and amino acids) too large for
channels
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• Binding of substrate causes shape change
in carrier then passage across membr |
Channel-Mediated Facilitated Diffusion | • Aqueous channels formed by
transmembrane proteins
• Selectively transport ions or water
• Two types:
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– Leakage channels
• Always open
– Gated channels
• Controlled by chemical or electrical signals |
Passive Processes: Osmosis | • Movement of solvent (e.g., water) across
selectively permeable membrane
• Water diffuses through plasma
membranes
Th h li id bil
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– Through lipid bilayer
– Through specific water channels called
aquaporins (AQPs)
• |
Passive Processes: Osmosis | • Water concentration varies with number of
solute particles because solute particles
displace water molecules
• Osmolarity - Measure of total
concentration of solute particles
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p
• Water moves by osmosis until hydrost |
Passive Processes: Osmosis | • When solutions of different osmolarity are
separated by membrane permeable to all
molecules, both solutes and water cross
membrane until equilibrium reached
When solutions of different osmolarity are
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• separated by m |
Importance of Osmosis | • Osmosis causes cells to swell and shrink
• Change in cell volume disrupts cell
function, especially in neurons |
Tonicity | • Tonicity: Ability of solution to alter cell's
water volume
– Isotonic: Solution with same non-penetrating
solute concentration as cytosol
Hypertonic: Solution with higher non-
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– nonpenetrating
solute concentration t |
Membrane Transport: Active Processes | • Two types of active processes
– Active transport
– Vesicular transport
• Both require ATP to move solutes across a
li i l b b
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living plasma membrane because
– Solute too large for channels
– Solute not lipid solubl |
Active Transport | • Requires carrier proteins (solute pumps)
– Bind specifically and reversibly with
substance
• Moves solutes against concentration
gradient
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– Requires energy |
Active Transport: Two Types | • Primary active transport
– Required energy directly from ATP hydrolysis
• Secondary active transport
– Required energy indirectly from ionic
di t t d b i ti t t
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gradients created by primary active transport |
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Primary Active Transport | • Energy from hydrolysis of ATP causes
shape change in transport protein that
"pumps" solutes (ions) across membrane
• E.g., calcium, hydrogen, Na+-K+ pumps |
Primary Active Transport | • Sodium-potassium pump
– Most well-studied
– Carrier (pump) called Na+-K+ ATPase
– Located in all plasma membranes
I l di i d d ti
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– Involved in primary and secondary active
transport of nutrients and ions |
Sodium-Potassium Pump | • Na+ and K+ channels allow slow leakage
down concentration gradients
• Na+-K+ pump works as antiporter
– Pumps against Na+ and K+ gradients to
maintain high intracellular K+ concentration
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and high extracellular Na+ co |
Cytoplasm | • Located between plasma membrane and
nucleus
– Composed of
• Cytosol
– Water with solutes (protein, salts, sugars, etc.)
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p , , g , )
• Organelles
– Metabolic machinery of cell; each with specialized
function; eithe |
Cytoplasmic Organelles | • Membranous
– Mitochondria
– Peroxisomes
– Lysosomes
E d l i ti l
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• Membranes allow crucial compartmentalization
– Endoplasmic reticulum
– Golgi apparatus
• Nonmembranous
– Cytoskeleton
– Centrioles
– Ribosomes |
Mitochondria | • Double-membrane structure with inner
shelflike cristae
• Provide most of cell's ATP via aerobic
cellular respiration
R i
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– Requires oxygen
• Contain their own DNA, RNA, ribosomes
• Similar to bacteria; capable of c |
Ribosomes | • Granules containing protein and rRNA
• Site of protein synthesis
• Free ribosomes synthesize soluble
proteins that function in cytosol or other
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organelles
• Membrane-bound ribosomes (forming
rough ER) synthesize pro |
Endoplasmic Reticulum (ER) | • Interconnected tubes and parallel
membranes enclosing cisterns
• Continuous with outer nuclear membrane
• Two varieties:
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– Rough ER
– Smooth ER |
Rough ER | • External surface studded with ribosomes
• Manufactures all secreted proteins
• Synthesizes membrane integral proteins
and phospholipids
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• Assembled proteins move to ER interior,
enclosed in vesicle, go to Golgi appar |
Smooth ER | • Network of tubules continuous with rough
ER
• Its enzymes (integral proteins) function in
– Lipid metabolism; cholesterol and steroidbased
hormone synthesis; making lipids of
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y gp
lipoproteins
– Absorption, synthes |
Golgi Apparatus | • Stacked and flattened membranous sacs
• Modifies, concentrates, and packages
proteins and lipids from rough ER
• Transport vessels from ER fuse with
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convex cis face; proteins modified, tagged
for delivery, sorted, pa |
Golgi Apparatus | • Three types of vesicles bud from concave
trans face
– Secretory vesicles (granules)
• To trans face; release export proteins by
exocytosis
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y
– Vesicles of lipids and transmembrane proteins
for plasma membrane or or |
Peroxisomes | • Membranous sacs containing powerful
oxidases and catalases
• Detoxify harmful or toxic substances
• Catalysis and synthesis of fatty acids
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• Neutralize dangerous free radicals (highly
reactive chemicals with unpaired |
Lysosomes | • Spherical membranous bags containing
digestive enzymes (acid hydrolases)
– "Safe" sites for intracellular digestion
• Digest ingested bacteria, viruses, and toxins
• Degrade nonfunctional organelles
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eg ade o u c o a |
Endomembrane System | • Overall function
– Produce, degrade, store, and export biological
molecules
– Degrade potentially harmful substances
Includes ER Golgi apparatus secretory
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• ER, apparatus, vesicles, lysosomes, nuclear and plasma
mem |
Cytoskeleton | • Elaborate series of rods throughout
cytosol; proteins link rods to other cell
structures
– Three types
• Microfilaments
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• Intermediate filaments
• Microtubules |
Microfilaments | • Thinnest of cytoskeletal elements
• Dynamic strands of protein actin
• Each cell has a unique arrangement of
strands
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• Dense web attached to cytoplasmic side of
plasma membrane is called terminal web
– Gives strengt |
Intermediate Filaments | • Tough, insoluble, ropelike protein fibers
• Composed of tetramer fibrils
• Resist pulling forces on cell; attach to
desmosomes
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• E.g., neurofilaments in nerve cells; keratin
filaments in epithelial cells |
Microtubules | • Largest of cytoskeletal elements; dynamic
hollow tubes; most radiate from
centrosome
• Composed of protein subunits called
tubulins
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• Determine overall shape of cell and
distribution of organelles
• Mitochondria, l |
Motor Proteins | • Protein complexes that function in motility
(e.g., movement of organelles and
contraction)
• Powered by ATP |
Centrosome and Centrioles | • "Cell center" near nucleus
• Generates microtubules; organizes mitotic
spindle
• Contains paired centrioles
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– Barrel-shaped organelles formed by
microtubules
• Centrioles form basis of cilia and flagella |
Cellular Extensions | • Cilia and flagella
– Whiplike, motile extensions on surfaces of
certain cells
– Contain microtubules and motor molecules
Cilia move substances across cell surfaces
Cellular Extensions
– – Longer flagella propel whole cells (tail of
sperm) |
Cilia and Flagella | • Centrioles forming base called basal
bodies
• Cilia movements alternate between power
stroke and recovery stroke |
Cellular Extensions | • Microvilli
– Minute, fingerlike extensions of plasma
membrane
– Increase surface area for absorption
Core of actin filaments for stiffening |
Nucleus | • Double-membrane barrier; encloses
nucleoplasm
• Outer layer continuous with rough ER and bears
ribosomes
• Inner lining ( nuclear lamina) maintains shape ofg ) p
nucleus; scaffold to organize DNA
• Pores allow substances to pass; nuclear pore
com |
Nucleoli | • Dark-staining spherical bodies within
nucleus
• Involved in rRNA synthesis and ribosome
subunit assembly
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• Associated with nucleolar organizer
regions
– Contains DNA coding for rRNA
• Usually one or two per cell |
Chromatin | • Threadlike strands of DNA (30%), histone
proteins (60%), and RNA (10%)
• Arranged in fundamental units called
nucleosomes
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• Histones pack long DNA molecules;
involved in gene regulation
• Condense into barlike bodie |
Cytosolic Protein Degradation | • Autophagy
– Cytoplasmic bits and nonfunctional organelles
put into autophagosomes; degraded by
lysosomes
• Ubiquitins
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– Tag damaged or unneeded soluble proteins in
cytosol
– Digested by soluble enzymes or proteasom |
Extracellular Materials | • Body fluids—interstitial fluid, blood
plasma, and cerebrospinal fluid
• Cellular secretions—intestinal and gastric
fluids, saliva, mucus, and serous fluids
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• Extracellular matrix—most abundant
extracellular material |
Developmental Aspects of Cells | • All cells of body contain same DNA but
cells not identical
• Chemical signals in embryo channel cells
into specific developmental pathways by
turning some genes on and others off
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• Development of specific and distinc |
Apoptosis and Modified Rates of Cell
Division | • During development more cells than
needed produced (e.g., in nervous
system)
• Eliminated later by programmed cell death
(apoptosis)
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– Mitochondrial membranes leak chemicals that
activate caspases |
Apoptosis and Modified Rates of Cell
Division | • Organs well formed and functional before
birth
• Cell division in adults to replace short-lived
cells and repair wounds
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• Hyperplasia increases cell numbers when
needed
• Atrophy (decreased size) results from
loss |
Theories of Cell Aging | • Wear and tear theory—Little chemical insults
and free radicals have cumulative effects
• Mitochondrial theory of aging—free radicals in
mitochondria diminish energy production
• Immune system disorders—autoimmune
y
responses; progressive weakening |
Theories of Cell Aging | • Most widely accepted theory
– Genetic theory—cessation of mitosis and cell
aging programmed into genes
• Telomeres (strings of nucleotides protecting ends
of chromosomes) may determine number of times
a cell can divide
• Telomerase lengthens telom |